Pyrotechnic fuse

ABSTRACT

A substantially uniform pyrotechnic fuse is provided by using particulate pyrotechnic mixture compacted in a small tubing. By preselecting the pyrotechnic mixture, the fuse can have a burning rate up to 35 seconds per inch. The pyrotechnic fuse material can also be preselected to provide either a flexible or substantially rigid fuse structure.

limited States Patent 1191 Richardson et al.

[ 1 Jan. 23, 1973 [54] IPYROTECHNIC FUSE 3,382,121 5/1968 Sherlock ..l56/86 3,424,630 1/1969 Corley ..l49/19 [75] Inventors. Jack Y. IRICIIIaIFSOII, Mouth-of-Wil- 3,344,003 9/1967 Miranda etaL Mug/19 e Mellow stanhope 3,529,042 9/1970 Lippert ..149/19 [73] Assignee: Brunswick Corporation, Chicago, OTHER PUBLICATIONS Ill. TM 9-1916 to, Department of the Army, Military Ex- [22] Filed: March 12, 1970 plos1ves, pp. 255-259 relied on UF 523A5l 1955 C4. [21] Appl. No.: 6,750 Primary Examiner-Verlin R. P'endegrass Attorney-Donald S. Olexa, Jerome M. Teplitz, John 521 U.S. c1. ..l02/27R g i g i -d Ia C Ld rand HOfgren, 51 1111.131 ..F42h 3/10 egne" man c [58] Field of Search ..l02/27, 70, 85, 86.5; 86/1;

149/19; 156/86 [57] ABSTRACT I A substantially uniform pyrotechnic fuse is provided [56] R fer n s Cit d by using particulate pyrotechnic mixture compacted in a small tubing. By preselecting the pyrotechnic mix- UNITED STATES PATENTS ture, the fuse can have a burning rate up to 35 2,418,769 4/1947 seconds per inch. The pyrotechnic fuse material can 2,513,391 7/1950 also be preselected to provide either a flexible or sub- 3,050,429 8/1962 stantially rigid fuse structure. 3,325,325 6/1967 3,367,266 2/1968 16 Claims, 8 Drawing Figures PYROTECHNIC FUSE BACKGROUND OF THE INVENTION l. Field of the Invention This invention is in the field of pyrotechnics, and more particularly in the field of pyrotechnic fuse trains.

2. Description of the Prior Art It is well known that fuse burning rates are determined by the composition of the pyrotechnic mixture, the packing density, the encapsulating or impregnating associate material, and in some instances the mechanical gadgetry in combination therewith. One way in which a burning rate of a pyrotechnic fuse mixture can be retarded is to compact the particulate pyrotechnic mixture into a very dense composite. In order to subject the particulate mixture to the high pressures neces sary to form the denser composition, means must be provided to support the particulate mixture during compaction and keep it in a usable shape after compaction. The simplest means to provide this support is to use a metal tube, which can be filled with a particulate compacted pyrotechnic mixture. One method which has been used to compact a particulate mixture into a tube is to employ a device using a plunger attached to a movable head of a press. The plunger is inserted into the tube filled with the loose particulate mixture. The plunger compresses the mixture packing it tightly in the tube. However, it is known to those skilled in the art of powder metal technology that when a length to diameter ratio of a column of compacted powders or particulate matter starts to increase, the density of the compacted powder varies. This phenomena is shown in FIG. 7 (and noted as prior art) wherein a compacted powder column is graphically depicted. The two ends of the column are denoted as 26 and 28, the middle of the column denoted as 30. The curve 32 is a representative plot of the density of the compacted powder. It can be observed from the graph that the density of the powder compact is much less in the middle 30 then at the ends 26 and 28 of the column. Thus, a pyrotechnic fuse mixture compacted in such a fashion would have a non-uniform burning rate. I

It is well known in the art that it is possible to provide a substantially uniformly dense column of compacted powder by incrementally compacting the powder in the tube; however, this process proves to be very tedious and time consuming. When long (over 1 inch) particulate pyrotechnic fuses are compacted in metal tubes having a diameter of less than one-fourth inch, the burning gases and vapors must be forced out of the open end of the tube. To this end the burning rate of the exiting gases must be increased thereby producing greater pressures to force these gases out of the tube. Consequently, this progressively increasing burning rate provides both faster and non-uniform burning. Therefore, it has been found that this is a self-defeating method to form a uniformly slow burning fuse.

In addition, the metal tubing of the fuse acts as a heat sink thereby drawing heat from the burning pyrotechnic mixture. The flame temperature of the pyrotechnic mixture must therefore be increased to sustain burning which is also self-defeating because as the flame temperature is increased to compensate for the heat loss an increased burning rate is undesireably achieved. It would be obvious to those skilled in the art that a non-metallic tube could be substituted for a metal tube thereby eliminating the metal heat sink problem. However, as a diameter to length ratio increased there would be practical limitations as to just how long a column of powder could be packed into a non metallic tubing (reference should be had to prior art FIG. 7). For example, it would be uneconomical, difficult and self-limiting to compact either a metallic or non-metallic tubing having an inside diameter of less than one-quarter inch and a length of more than 1 inch for the same reasons mentioned above. If a non-rigid or flexible tubing 42 were compacted in the above mentioned manner, the flexibility of the tube material would prove to be unsatisfactory because the pliability of the tubing walls 44 would permit internal bulging and non-uniform compacting of the pyrotechnic mixture 46 as shown in FIG. 8 (also prior art) even though supported by a die 40. In addition, the prior art indicates that the encapsulating material must burn at the same rate as the pyrotechnic fuse mixture in order to have a controlled rate of burning. However, if the encapsulating material burns at a slower rate, the mixture must be hotter" to keep the fuse burning, and if the encapsulating material has a faster burn rate than the pyrotechnic mixture, the fuse will not burn uniformly or controllably as a fuse.

To circumvent the limitations of providing a slow burning pyrotechnic fuse, it is a generally accepted practice to combine a short (usually 1 inch or less) pyrotechnic fuse in combination with expensive and usually complicated mechanical devices to provide a relatively constant composite pyrotechnic fuse. The mechanical reliability of these devices can be very high, but the cost is greatly increased to provide a high level ofquality assurance.

SUMMARY OF THE INVENTION This invention relates to slow buzming fuse trains and is concerned with a new and novel pyrotechnic fuse that has pre-selected burning rate.

It is an object of this invention to provide a long economical slowburning pyrotechnic fuse made from a fuel-oxidizer combination and radially compacted by an enclosure whereby equal compacting pressure is ex erted substantially uniformly on all the fuel-oxidizer over the whole length of the enclosure and providing a substantially uniform density therein.

Another object of this invention is the provision for such a pyrotechnic fuse that can have a burning rate from approximately 5 seconds per inch to approximately 35 seconds per inch.

Another object of this invention is the provision for such a pyrotechnic fuse that may be flexible and arranged in any desired configuration.

Yet another object of this invention is the provision for such a fuse to generate a progressive orifice in the enclosure tubing as the fuse burns and thereby provide an exit gas port adjacent to the burning flame front of the fuel-oxidizer mixture.

Still another object of this invention is the provision for such a fuse that the fuel and oxidizer may be rigidified after being radially compressed.

Still yet another object of this invention is the provision for such a rigidifiable fuse that may be shaped into any desired shape prior to becoming rigid.

Thus, this invention provides a small diameter uniformly slow burning pyrotechnic fuse. The fuse can be of any desired length in either flexible form or formed into any selected configuration and subsequently become rigid. A uniformly dense pyrotechnic mixture is formed when it is compacted in a unique structural enclosure. It has been found that this slow burning pyrotechnic mixture can be used to provide a fuse that will burn at any desired rate, such as from 1 inch in seconds to 1 inch in 35 seconds.

The above and other and further objects and features will be more readily understood by reference to the following detailed description and the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of one embodiment of the fuse;

FIG. 2 is a cross-sectional view of FIG. 1',

FIG. 3 is a perspective view of a coiled fuse tube;

FIG. 4 is a perspective view of a serpentine configuration of the fuse tube;

FIG. 5 is another perspective view of the fuse tube;

FIG. 6 is a cross-sectional view of another tubular embodiment of the fuse;

FIG. 7 is a graphic representation of the density variation of a particulate powder compacted in a length of tubing; and

FIG. 8 is a cross-sectional view of a flexible tubing axially compacted with a particulate material while the tubing is held in a restraining die.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In one preferred embodiment of the invention, a flexible tube or enclosure 12 encapsulating a pyrotechnic mixture 14 is shown as fuse 10 in FIG. 1, although any shape enclosure may be used, as desired. The pyrotechnic mixture 14 comprises at least a fuel portion and an oxidizer portion and is in particulate form.

The tube 12 is a heat shrinkable thermoplastic resin such as polyvinylchloride, polyethylene, tetrofluroethylene(Teflon) or any other heat shrinkable polymer.

It is fully contemplated that any energy shrinkable non-metallic material can be utilized to form the enclosure 12 such as a thermoplastic polymer that-is shrinkable by applying radiation energy, e.g. ultraviolet radiation, x-ray radiation, gamma radiation, etc.

The particulate pyrotechnic mixture 14 is inserted into the tubing by any convenient method such as vibratory filling, funneling, extruding, suctioning, exuding, as desired. In one illustrative embodiment the tubing 12 filled with the particulate pyrotechnic mixture 14' is exposed to radiation energy such as infra-red radiation in the temperature range of 150 to 200 C. for approximately 10 to seconds to stress relieve the tubing. However, it has been found that lower temperatures may be used if longer exposure times are employed. In addition, shorter exposure times may be used if higher temperatures are utilized provided that the highest temperature used is below the instantaneous auto-ignition temperature of the pyrotechnic mixture l4.

The enclosure or tube 12 is formed of a prestressed thermoplastic resin material and filled in with the particulate pyrotechnic mixture 14 while in a prestressed state. Heating the tubing 14 causes the inherent stresses to seek to achieve an unstressed or stress relieved condition. The prestressed tubing 14 has a diameter that is larger than the tubing in its stressed relieved or unstressed condition. When the prestressed tubing is stress relieved it shrinks in sizespecifically, the diameter becomes smaller by constricting.

When heat is applied to the tubing 12 filled with the porous particulate pyrotechnic mixture 14, the tubing attempts to achieve a stressed relieved condition and thereby constrictively compacting the pyrotechnic mixture therein. These inwardly radial compacting forces are represented by the arrows 16 in FIG. 2 wherein FIG. 2 is a cross section of the fuse 10 in FIG. 1. Consequently, the constricting forces exerted on the pyrotechnic mixture caused by stress relieving the tubing compacts the pyrotechnic mixture into a much denser material which has a substantially uniform porosity or density extending over the length of the tube. By this means it is possible to constrict long flexible columns that can range from I inch to 50 feet or more and thereby provide extremely long slow burning fuses.

It has been found that by compacting the pyrotechnic mixture, the fuse l0 burns at a much slower rate than the same pyrotechnic mixture that is not compacted. Additionally, such a fuse burns at a subatantially more uniform rate. The compacted tube fuse 10, so formed, still remains flexible and can be arranged in any desired configuration, such as the coiled shaped fuse 18 shown in FIG. 3 or the serpentine shaped fuse 20 shown in FIG. 4. In one embodiment of the invention, a slow burning fuse can be achieved because as the pyrotechnic mixture burns, it forms a progressively generated orifice at the flame front along the surface of the tube providing an immediate escape path for the gases and vapors out the side of the fuse tube; therefore, the fuse burns at a constant rate and pressure. Illustratively, as shown in FIG. 5, the progressively generated orifice 22 is formed as the heat from the burning pyrotechnic mixture 14a selectively heats the tubing 12a. The burning gases and vapors 24 exhaust from the progressive orifice 22 as they are generated and the orifice provides an escape route for the burning gases and vapors instantaneously. Since this exit route is formed instantaneously, certain components such as vaporizable dyes can be used as coolants exhausting before the dye reaches its decomposition temperature. Thus, a means is provided to permit visual observation of the burning rate of the fuse.

In another embodiment of the invention shown in FIG. 6, a cross-section of a flexible tube 12b has an internally grooved wall portion 34. The use of this configuration of tubing provides a method of preselecting and predetermining the path and rate of the fame fronts progressive orifice 22.

The pyrotechnic mixture 14 comprises fuels, oxidizers and in some instances coolants. The fuel portion may be of the following materials; (1) organic compounds, i.e., carbon black, charcoal, cellulose, sugar, thermosetting polymers (e.g., epoxy resin, polyurethanes, vulcanized elastomers, etc.), thermoplastic resins (e.g., polyvinylchloride, parafin polyvinylalcohol, etc.); etc., (2) metals in particulate form, i.e., aluminum, magnesium, tungsten, zirconium, silicon, etc.; and, (3) non-metallic elements in particulate form, i.e., sulfur, phosphorus, etc. The oxidizer portion may be made from at least one of the following materials; (l) inorganic salts, i.e., KNO NaClO NH ClO etc.; (2) metal oxidizers, i.e., Pb O PbO, ZNO, etc.; and, (3) halocarbons, i.e., tetrafluorethylene, dechlorane, etc. It is fully contemplated that other materials may be used as the fuel or oxidizer portion as long as they provide a proper burning rate.

A coolant material may be added to the fuel-oxidizer portions of the pyrotechnic mixture in order to provide a specific result such as retard the burning rate, generate a color as the fuel-oxidizer portion burns to observe the flame front, or any desired effect.

lllustratively, the coolant may be made from at least the following types of materials; (1) vaporizable organic compounds, i.e., organic dyes, orthochlorobenzal malononitrile, etc., and (2) thermally unstable salts that produce gases on decompositions, i.e., carbonates, bicarbonates, etc.

In one embodiment of the invention, a fuel and oxidizer are both crushed to form fine powder. Proper proportions of the fuel and oxidizer are mixed together to form the pyrotechnic mixture that will have the desired burning rate. The mixture is packed into a heat shrinkable tubing. The filled tubing is heated to cause it to shrink and thereby radially compacting the pyrotechnic mixture. Since the tubing is axially flexible and the compaction of the powdery pyrotechnic mixture is radial, the tube fuse remains flexible after compacting the pyrotechnic mixture. Therefore, the fuse can be oriented to take a plurality of configurations. lt has been found that within certain broad limitations that if the same pyrotechnic mixture is placed in a tubing having an inside diameter of from about 0.015 inch to about 2 inches, that the fuse will burn at the same rate as long as the compacting pressures are essentially equal and the particulate pyrotechnic mixtures are substantially uniformly dense. However, the amount of heat in BTUs that is produced by the fuse will be greater in the 2 inch diameter fuse than the smaller 0.015 inch diameter tubing.

' In another embodiment of the fuse, an epoxy resin fuel is combined with an oxidizer to form the pyrotechnic mixture. The oxidizer is a powder while the epoxy resin is a liquid. The two (fuel and oxidizer) are mixed together and injected into a heated shrinkable tubing. The ends of the tubing may be closed, if desired, and the tubing is heated. Under heat the tubing shrinks compressing the epoxy-oxidizer mixture. The epoxy can be either a long or short curing material as desired. After the tubing is shrunk, the fuse can be arranged in any desired geometric configuration prior to the epoxy hardening. The use of the epoxy as the fuel provides a fuse that can be pre-shaped into any desired geometric configuration prior to hardening. Thus, a fuse can be formed that retains its geometric shape as well as being mass produced. The epoxy fuel fuse burns forming the same progressive orifice as the compacted particulate pyrotechnic mixture to provide an escape means for the gases and vapors. It has also been found that the epoxy-fuel fuse will burn uniformly without the need of forming a progressively generated orifice and therefore will burn under water.

The following examples are of specific fuses made in accordance with this invention, but should not be construed in any way to limit the scope contemplated by this invention.

EXAMPLE I A mixture A was formulated by blending 36.9 parts by weight of a particulate red dye (per mil. spec. D-37l8A) with 25 parts by weight of nitrocellulose lacquer (8 percent nitrocellulose and 92 percent acetone) until the dye was thoroughly wetted by the lacquer. The wetted dye was then mixed with 32.] parts by weight of KClO 16.1 parts by weight NaHCO and 12.4 parts by weight of sulphur until a granular form was achieved. The composite mixture A was heated for approximately 8 hours at approximately 140 F. so that the acetone was driven off. The dried mixture A was sifted through a 40-mesh screen making a final mixture A A mixture B was formulated by blending parts by weight of silicon with 480 parts by weight of red lead (Pb O until homogeneous. A blend of 36 parts by weight of diatomaceous earth was wetted by 127.5 parts by weight of nitrocellulose lacquer (8 percent nitrocellulose and 92 percent acetone) and then thoroughly mixed with the silicon red lead. The mixture B was granulated and then heated for approximately eight hours at approximately F. to remove the acetone. The dried mixture B was also sifted through a 40-mesh screen making a final mixture 8" The final fuse mixture was formed by adding 3 parts by weight of the final mixture A with 1 part by weight of of the final mixture 8" The mixing method used provided a final fuse mixture wherein the mixture A particles were thoroughly intermixed with the final mixture 8" particles. A carbon-loaded polyvinylchloride heat-shrinkable tubing having an 0.1 15 inch outside diameter, a 0.095 inch inside diameter, and a length of 6 inches was vibratorily filled with the final fuse mixture. The filled tubing was placed in an oven having a temperature of approximately C. for approximately 40 seconds to shrink the tubing and constrictively compact the fuse mixture. The compacted tubing was arranged in a coiled configuration. The fuse was ignited and exhibited a burning rate of 31 seconds per inch.

EXAMPLE II The final fuse mixture of Example I was vibratorily packed into a 6-inch length of carbon-loaded polyvinylchloride tubing having a 0.215 inch outside diameter and a 0.195 inch inside diameter heat-shrinkable tubing. The filled tubing was placed in an oven having a temperature of approximately 200C. for approximately 20 seconds to heat shrink the tubing and constrictively compact the final fuse mixture. The fuse tubing was ignited and exhibited a burning rate of 30 seconds per inch.

The filled heat-shrunk tubing of both Examples 1 and [I were extremely flexible. In subsequent tests of constrictively compacted pyrotechnic. fuses made in accordance with Example I and Example 11, one end of the tubing was sealed, and the tubing ignited exhibiting a burning rate ranging from 25 seconds per inch to 35 seconds per inch depending upon the shrink time for the tubing and the amount of pyrotechnic mixture used.

EXAMPLE I An epoxy resin having a composition of approximately 25 percent curing agent (hardener) and 75 percent base resin made by the Hysol Corporation and sold as hardener No. H2-356l and base resin No. R9-2039 was thoroughly blended with ammonium perchlorate in the ratio of 1 part epoxy resin and 3 parts ammonium perchlorate to form a thick fueloxidizer fuse mixture. A 3 inch length of 0.115 inch outside diameter, 0.0095 inch inside diameter carbonloaded polyvinylchoride tubing was filled with the thick fuse mixture. The filled tubing was placed in an oven having a temperature of approximately 150 C. with the tubing remaining in the oven for approximately seconds to shrink the tubing and compress the fuse mixture. The fuse tubing was removed from the oven in a flexible condition. The tubing was preshaped in a serpentine configuration and the epoxy resin allowed to harden, thus forming a solid pre-shaped fuse. The fuse was then ignited and immediately placed in water wherein the fuse exhibited a burning rate of approximately seconds per inch while completely submerged in the water.

it has been found that certain epoxy resins may be used to provide the slow burning pyrotechnic fuse without the separate step of shrinking the filled tubing in an oven or other such heating device. These epoxies exhibit an exothermic reaction when the hardener and the base resin are mixed together which produces sufficient heat to shrink the tubing. lllustratively, the epoxyoxidizer combination is shown as 14b in FIG. 6.

Although specific embodiments and variations of the invention have been described, many modifications and changes may be made in the configurations of the tubing, the combinations of fuels, oxidizers and coolants (when desired) which would increase the burning rate beyond seconds per inch and in the materials used to make the enclosure without departing from the spirit and scope of the invention as defined in the appended claims. We claim: I. A pyrotechnic fuse structure comprising: a. a flexible non-metallic plastic radially heat shrinkable tubular enclosure having a longitudinal internally grooved wall portion;

b. a pyrotechnic burnable portion located within and filling the tubular enclosure and comprising a fueloxidizer mixture; and

c. means for radially compressing the fuel-oxidizer mixture into a substantially uniformly dense material having a substantially constant burn rate.

2. The fuse of claim 1 wherein said enclosure material is loaded with carbon black.

6. The fuse of claim 1 wherein said fuse upon burning propagates a progressive orifice through the wall of said enclosure.

7. The fuse of claim 6 wherein said orifice is formed adjacent to said burning flame front.

8. The fuse of claim 1 wherein said fuel is in a finely divided particulate form.

9. The fuse of claim 1 wherein said oxidizer is in a finely divided particulate form.

10. The fuse of claim 1 wherein said fuel and oxidizer are blended with a particulate coolant.

11. The fuse of claim I wherein said fuel is a thermosettingresin.

12. The fuse of claim 1 wherein said'fuel and oxidizer comprises a mixture of oxidizer in particulate form and a thermosetting resinous fuel.

13. The fuse of claim 12 wherein said enclosure is arranged in a preselected configuration.

14. The fuse of claim 13 wherein said enclosure is in a serpentine configuration.

15. The fuse of claim 13 wherein said enclosure is in a coiled configuration.

16. A method of making a pyrotechnic fuse comprising the steps of:

a. filling a flexible energy shrinkable tubing with a fuel-oxidizer mixture in particulate form; b. radially shrinking the tubing by radiation energy;

and c. compressing the fuel-oxidizer mixture into a substantially uniformly dense particulate material. 

2. The fuse of claim 1 wherein said enclosure remains flexible subsequent to compressing said fuel and oxidizer.
 3. The fuse of claim 1 wherein said fuse has a burn rate of approximately 15 seconds to 30 seconds per inch.
 4. The fuse of claim 1 wherein said enclosure is made of polyvinylchloride material.
 5. The fuse of claim 4 wherein said polyvinylchloride material is loaded with carbon black.
 6. The fuse of claim 1 wherein said fuse upon burning propagates a progressive orifice through the wall of said enclosure.
 7. The fuse of claim 6 wherein said orifice is formed adjacent to said burning flame front.
 8. The fuse of claim 1 wherein said fuel is in a finely divided particulate form.
 9. The fuse of claim 1 wherein said oxidizer is in a finely divided particulate form.
 10. The fuse of claim 1 wherein said fuel and oxidizer are blended with a particulate coolant.
 11. The fuse of claim 1 wherein said fuel is a thermosetting resin.
 12. The fuse of claim 1 wherein said fuel and oxidizer comprises a mixture of oxidizer in particulate form and a thermosetting resinous fuel.
 13. The fuse of claim 12 wherein said enclosure is arranged in a preselected configuration.
 14. The fuse of claim 13 wherein said enclosure is in a serpentine configuration.
 15. The fuse of claim 13 wherein said enclosure is in a coiled configuration.
 16. A method of making a pyrotechnic fuse comprising the steps of: a. filling a flexible energy shrinkable tubing with a fuel-oxidizer mixture in particulate form; b. radially shrinking the tubing by radiation energy; and c. compressing the fuel-oxidizer mixture into a substantially uniformly dense particulate material. 